[ 161 3 
would fignify fo many degrees decreafe of heat, 
and the barometer would fink by — v The 
fixt temperature of heat, to which M. de luc 
thought beft to reduce his obfervations of the ba- 
rometer, is i-th of the interval from freezing to 
boiling water above the former point : and if the 
thermometer was higher than this degree, he 
B H 
fubftra&ed — X ^ 5 if it was lower, he added it 
54 
to the obferved height of the barometer ; and 
thus he obtained the exadl height of the barome- 
ter, fuch as it would have been, if the denfity of 
its quickiilver had been the fame as anfwers to 
the fixt degree of temperature. He thus correc- 
ted the height of both his barometers (that at the 
bottom, and that at the top of the hill) for the 
particular degree of heat, indicated by a thermo- 
meter attached to the barometer, at each ftation ; 
for it might and would commonly happen, that 
the degree of heat would be different at the two 
flations. The heights of the barometers, thus 
corredted, were what he made ufe of in his fub- 
fequent calculations. Calling thefe two altitudes 
of the barometer B and b , putting log. B and 
log. b , for the logarithms of B, and b, taking 
only the four firft places of figures, after the charac- 
teriftic, or confidering the remaining figures as 
decimals, and putting C for the mean height of 
a thermometer, expofed to the air at top and bot- 
tom of the hill, the freezing point being o, and 
the point of boiling water at 8o, he finds, by his 
experiments, that the height of the hill will be 
given in French toifes, when C is i6f, by 
Vol. LXIV. " Y Amply 
